Passive optical network address association recovery

ABSTRACT

Techniques for reestablishing network address associations upon recovery of a passive optical network (PON) disablement relay on storage address association information. A network node stores address association information in non-volatile memory upon detecting a network disablement. Upon recovery of the PON from the disablement, the network node associates network addresses to clients in accordance with the address association information. The network node may further verify the associations by sending ARP queries for the network addresses to the associated clients. Alternatively, the network nodes may reestablish the address associations by tracking the length of time of the network disablement, and updating address association information in accordance with the length of the disablement.

[0001] This application claims priority from U.S. provisionalapplication serial No. 60/421,206, filed Oct. 24, 2002, the entirecontent of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] The invention relates to computer networking and, moreparticularly, to network address associations within a passive opticalnetwork (PON).

BACKGROUND

[0003] A passive optical network (PON) can deliver voice, video andother data among multiple network nodes using a common optical fiberlink. Passive optical splitters and combiners enable a number of networknodes to share the optical fiber link. Each network node terminates theoptical fiber link for a residential or business subscriber, and issometimes referred to as a subscriber premises node. A PON typicallyincludes a PON interface having multiple, independent PON interfacemodules that serve multiple optical fiber links. In the case of dataservices, the PON interface receives data packets from an Internetservice provider for transmission to network nodes. A PON interfacemodule provides an Ethernet interface for transmission and reception ofdata over a particular optical fiber link that serves a group of networknodes.

[0004] Dynamic Host Configuration Protocol (DHCP), or other similarprotocols, can be used to assign Internet Protocol (IP) addresses toclients represented by network nodes within a PON. For example, anetwork node may associate a DHCP-assigned IP address with a clientrepresented by the node. The association of an IP address with a clientexists for the duration of a lease time defined by a DHCP server, oruntil the client releases the IP address. In the event the PON istemporarily disabled, however, the IP address association recognized bythe DHCP client and DHCP server may inadvertently be lost. In this case,the disablement may require manual intervention to reacquire the IPaddresses and reestablish the association for the DHCP server andclient.

SUMMARY

[0005] In general, the invention is directed to recovery of addressassociations within a passive optical network (PON) following a networkdisablement. Upon detection of a network disablement, one or morenetwork nodes within the PON store address association information innon-volatile memory. Address association information may include leasednetwork addresses, media access control (MAC) addresses of the clientsthat leased each of the network addresses, and a remaining lease timefor each network address. The network nodes may also store other addressassociation information such as a subnet mask associated with theclient, and a network address for a DHCP server that assigned the IPaddress.

[0006] Upon PON recovery, the PON reestablishes the association ofnetwork addresses to clients. For example, the network nodes mayretrieve the address association information from non-volatile memory.Based on the address association information, the network nodesreacquire the IP addresses and reestablish the association of networkaddresses to clients. During the network disablement, however, one ormore of the address associations may have ended. For instance, the leasetime for an address may have expired during the network disablement.

[0007] For this reason, the network nodes may be configured to verifywhether the address associations are still valid prior to reestablishingthe associations. For example, a network node may be configured to sendan Address Resolution Protocol (ARP) query for an IP address to anassociated client. The network node may send the ARP query to theassociated client periodically for the extent of any remaining leasetime indicated in the address association information.

[0008] An ARP response from the respective client demonstrates that theaddress association still exists, and indicates that the network nodemay maintain the designated address association for the client. Thus,the network node may be capable of verifying associations, andmaintaining the associations when an ARP response is received. The PONmay maintain the association of network addresses to clients until anARP response is not received from the client, or the remaining leasetime expires. Network nodes may further modify the association upondetecting a DHCP renewal response, detecting a new DHCP acknowledgementwith the IP address from the DHCP server, or detecting a DHCP release bythe client.

[0009] Alternatively, the network nodes may reestablish the addressassociations using a clock or other timing device. For example, networknodes may determine the length of time of the network disablement, andincorporate a timestamp in the address association information stored innon-volatile memory to indicate the length of time. Upon PON recoveryfrom the disablement, the network nodes may retrieve the addressassociation information, and compare the timestamp with a time indicatedby the timing device to determine the length of time of the disablement.

[0010] In this manner, network nodes may be capable of determining arelative time for the network disablement, and thereby updating theremaining lease time in the address association information. Forexample, network nodes may reduce the remaining lease times indicated inthe address association information by the length of time of thedisablement, and reestablish the associations of network addresses toclients in accordance with the updated address association information.

[0011] In one embodiment, the invention provides a method comprisingdetecting a disablement of a passive optical network. The method furthercomprises storing address association information indicating associationof network addresses with network clients upon detecting the networkdisablement, and associating the network addresses and the networkclients based on the address association information upon recovery fromthe network disablement.

[0012] In another embodiment, the invention provides a method comprisingretrieving stored address association information indicating associationof network addresses with network clients upon recovery of a passiveoptical network from a network disablement. The method further comprisesassociating the network addresses to the clients based on the addressassociation information. The method also includes sending ARP queriesfor the network addresses indicated in the address associationinformation, and maintaining the associations indicated in the addressassociation information upon receiving ARP responses for the networkaddresses.

[0013] In an added embodiment, the invention provides a methodcomprising retrieving stored address association information indicatingassociation of network addresses with network clients upon recovery of apassive optical network from a network disablement. The method furtherincludes determining a length of time of the disablement, and updatingremaining lease times indicated by the address association informationin accordance with the determined length of time of the networkdisablement. The method further includes associating the networkaddresses to the network clients in accordance with the updated addressassociation information.

[0014] In a further embodiment, the invention provides a passive opticalnetwork comprising a network node that represents at least one client.The passive optical network further comprises an interface thattransmits information to the network node via an optical fiber link. Thenetwork node stores a set of address association information thatassociates network addresses to the clients represented by the networknode.

[0015] In other embodiments, the invention provides computer-readablemedia comprising instructions for performing the techniques describedherein.

[0016] The invention may provide one or more advantages. For example,the techniques described herein permit recovery of associations betweennetwork addresses and clients following a PON disablement with little orno manual intervention. In this manner, the invention can significantlyreduce system maintenance costs and downtime. In addition, in someembodiments, the techniques may promote cost efficiency by avoiding theuse of time devices, such as a real-time clock.

[0017] The details of one or more embodiments of the invention are setforth in the accompanying drawings and the description below. Otherfeatures, objects, and advantages of the invention will be apparent fromthe description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

[0018]FIG. 1 is a block diagram illustrating a passive optical network(PON) arranged to deliver information to a number of network nodes viaoptical fiber links.

[0019]FIG. 2 is a block diagram illustrating a PON with multiple clientscoupled to network nodes.

[0020]FIG. 3 is a block diagram illustrating an exemplary data structurefor arrangement of address association information.

[0021]FIG. 4 is a flow diagram illustrating a technique for maintainingaddress associations.

[0022]FIG. 5 is a flow diagram illustrating a technique forreestablishing address associations upon recovery of a PON from anetwork disablement.

[0023]FIG. 6 is a flow diagram illustrating a technique forreestablishing address associations using a timing device upon recoveryof a PON recovering from a network disablement.

DETAILED DESCRIPTION

[0024]FIG. 1 is a block diagram illustrating a passive optical network(PON) 10. In accordance with the invention, PON 10 may be configured toimplement techniques for recovery of address associations within the PONfollowing a network disablement. PON 10 may be arranged to delivervoice, data and video content (generally “information”) to a number ofnetwork nodes 11A-11D (collectively network nodes 11) via optical fiberlinks 12A-12N (collectively optical fiber links 12).

[0025] Exemplary components for implementing some of the features of PON10 are commercially available from Optical Solutions, Inc., ofMinneapolis, Minn., and designated by the trade name Fiberpath 400™,including the Fiberdrive™ headend bay interface and the Fiberpoint™subscriber premise nodes. Other components may be added or modified asdescribed herein to support techniques for recovery of addressassociations, in accordance with the invention.

[0026] As shown in FIG. 1, PON 10 includes a PON interface 13 thatreceives information from a source, and distributes the informationalong optical fiber links 12 to groups of network nodes 11. For example,PON interface 13 may receive voice information from the public switchedtelephone network (PSTN) 14 via a switch facility 16. In addition, PONinterface 13 may be coupled to one or more Internet service providers(ISP's) 18 via a router 20 and the Internet.

[0027] As further shown in FIG. 1, PON interface 13 may receive videocontent 22 from video content suppliers via a streaming video headend24. In each case, PON interface 13 distributes the information alongoptical fiber links 12 to groups of network nodes 11. A group of networknodes 11 may refer to nodes served by PON interface 13 and, moreparticularly, nodes served by a corresponding PON interface modulewithin PON interface 13 via a common optical fiber link 12. A group ofnetwork nodes 11 may include a single network node 11, or numerousnetwork nodes 11.

[0028] Network nodes 11, sometimes referred to as optical networkterminators (ONTs) or optical network units (ONUs), may include hardwarefor receiving information from PON 10 via optical fiber links 12, anddelivering the information to one or more client devices associated witha node 11. For example, each network node 11 may serve as a PON accesspoint for one or more clients. Clients may include a variety of clientdevices such as computers, network appliances, televisions, set-topboxes, wireless devices, or the like.

[0029] Network nodes 11 also may include hardware for transmittinginformation from the associated client devices over PON 10. For example,a network node 11 may transmit voice information over PSTN 14 via PONinterface 13 and switch facility 16 in the course of a telephoneconversation. In addition, a network node 11 may transmit data to avariety of network nodes on the Internet via ISP 18, router 20 and PONinterface 13. Multiple network nodes 11 typically transmit over a commonoptical fiber link 12 using time division multiplexing techniques.

[0030] In some embodiments, optical fiber link 12 may include a pair ofoptical fibers, forming an outgoing link and an incoming link. Forexample, the outgoing fiber optic link may transmit information from PONinterface 13 to network nodes 11. The incoming fiber optic link maytransmit information from network nodes 11 to PON interface 13.

[0031] PON interface 13 may be located near or far from a group ofnetwork nodes 11. In some existing networks, however, PON interface 13may reside in a central office situated within approximately ten milesfrom each network node 11. A network node 11 may be located at any of avariety of locations, including residential or business sites. Inaddition, a single network node 11 may operate on a shared basis todeliver information to clients within two or more closely locatedresidences or businesses via copper cabling, wireless communication, oradditional optical fiber connections, either directly or via a networkhub, router or switch.

[0032] PON 10 may lease network addresses, such as Internet Protocol(IP) addresses, to clients represented on network nodes 11. Furthermore,network nodes 11 may associate the leased network addresses with clientsthat requested the network addresses. For example, PON 10 may rely onone or more Dynamic Host Configuration Protocol (DHCP) servers (notshown in FIG. 1) to assign IP addresses to DHCP clients. The associationof IP addresses to clients exists for the duration of the lease timedefined by the DHCP server, or until the client releases the IP address.In accordance with the invention, PON 10 may be configured to supporttechniques for recovery of network address associations following atemporary disablement of PON 10. The recovery techniques enable theclients to reacquire previously assigned IP addresses. In addition, therecovery techniques enable PON 10 to reestablish the association of IPaddresses to corresponding nodes 11 with little or no manualintervention, reducing labor time and costs.

[0033] Upon detection of a network disablement, network nodes 11 storeaddress association information in non-volatile memory. The addressassociation information may indicate association of network addresseswith network clients, and may include leased network addresses, MACaddresses of the clients that leased the network addresses, and theremaining lease time applicable to each network address. Network nodes11 may also store other address association information such as a subnetmask associated with the client, and a network address for a DHCP serverthat assigned the IP address. Alternatively, PON interface 13 or someother network component within PON 10 may store the address associationinformation. The non-volatile memory that stores the associationinformation may include Read-Only Memory (ROM), Programmable Read-OnlyMemory (PROM), Erasable Programmable Read-Only Memory (EPROM),Electrically Erasable Programmable Read-Only Memory (EEPROM), FLASH,Non-Volatile Random Access Memory (NVSRAM), and Ferroelectric RandomAccess Memory (FeRAM), and the like.

[0034] Upon recovering from the network disablement, PON 10reestablishes the association of network addresses to clients. Forexample, network nodes 11 may retrieve the address associationinformation from the non-volatile memory upon detecting that PON 10 hasrecovered from the disablement. In accordance with the addressassociation information, network nodes 11 may associate networkaddresses to clients 36.

[0035] During the network disablement, however, one or more of theaddress associations may have ended. For instance, a lease time for aleased IP address may have expired. For this reason, network nodes 11may be configured to not only recover information about network addressassociations, but also verify whether the address associations are stillvalid. For example, a network node 11 may send an ARP query for arecovered IP address to an associated client 36. Network node 11 maysend the ARP query to the associated client 36 periodically for theextent of a remaining lease time indicated in the address associationinformation.

[0036] An ARP response from respective client 36 demonstrates that theaddress association still exists. In particular, the client 36recognizes the address identified by the ARP query and respondsaccordingly. Therefore, on the basis of the ARP response, network node11 may maintain the address association of the IP address to client 36.In this case, it is determined that the address associated is stillvalid, and that the pertinent lease time has not expired.

[0037] Network node 11 may verify each association, and maintain theassociations in which an ARP response was received, for all clientsattached to the network node, or at least those clients for whichassociation information has been stored. PON 10 maintains theassociation of network addresses to clients unless an ARP response isnot received from the client, or the remaining lease time expires.Network nodes 11 may further modify the association upon detecting aDHCP renewal response from a DHCP server, detecting a new DHCPacknowledgement with the IP address from the DHCP server, or detectingthat the client has released the leased address per the protocol.

[0038]FIG. 2 is a block diagram illustrating a PON 10 with multipleclients 36 coupled to each of network nodes 11. PON 10 includes PONinterface modules 30A-30M (collectively interface modules 30) within PONinterface 13. Each PON interface module 30, sometimes referred to as aline card, is coupled to a group of network nodes 11 via a fiber link12. PON interface 13 may include multiple PON interface modules 30, e.g.arranged in a common chassis. Each PON interface module 30 may form anindependent Ethernet interface that serves a group of network nodes 11coupled to a common optical fiber link 12. Hence, PON interface module30 and nodes 11 terminate opposite ends of optical fiber links 12.

[0039] Network nodes 11 may act as an interface between PON 10 and atleast one client 36. For example, a network node 11 may act as aninterface that allows information to transit from the optical fiberframework of PON 10 to an electrical metallic framework, such as acopper wire or coaxial cable client network. For instance, network node11 may interface the two frameworks by performing an opto-electricalconversion on information from PON interface modules 30 to clients 36.Network nodes 11 may also act as an interface for informationtransmitted in the opposite direction, i.e. from an electrical metallicframework to an optical fiber framework.

[0040] Each of network nodes 11 may further be responsible fordetermining which information is destined for clients 36 represented ona particular network node 11. PON interface 13 may transmit informationdestined to all network nodes 11 on optical fibers 12, and network nodes11 may retrieve only the information pertaining to clients 36represented on network nodes 1, e.g., by identification ofsource-destination IP address information in headers carried by thetransmitted packets.

[0041] PON 10 may use DHCP relay techniques, or other similartechniques, to provide IP addresses to clients 36 represented on networknodes 11. For example, when a client 36 requires an IP address, e.g.upon boot or lease expiration, client 36 transmits a DHCP request to anetwork node 11 representing the client. Network node 11 passes the DHCPrequest to the corresponding PON interface module 34. In response, therespective PON interface module 34 generates a DHCP proxy request onbehalf of client 36 and transmits it to an appropriate one of DHCPservers 37A-37J (collectively DHCP servers 37). DHCP servers 37 may, forexample, be maintained by an ISP that provides Internet service tovarious network nodes 11 in PON 10.

[0042] DHCP server 37 assigns an IP address to the requesting client 36,and forwards a DHCP acknowledgement with the IP address to requestingclient 36 via PON 10. The assigned IP address typically will have afinite lease time. Upon assignment of the IP address, network node 11representing client 36 may associate the leased IP address with therequesting client 26. For example, network node 11 may recordassociation information (ASSOC INFO) 38, which may include leased IPaddresses, the MAC addresses of the respective clients leasing the IPaddresses, the remaining lease times of leases, subnet masks associatedwith the client, or the like. Further, network node 11 may update an ARPcache that maps leased IP addresses with the MAC addresses of theclients leasing the IP address. The ARP cache may be used for routinginformation to clients.

[0043] Upon a network disablement, such as loss of power or otherfailure, PON interface 13 may lose state information indicating theaddress association of network addresses to clients 36. In accordancewith the invention, however, PON 10 supports recovery techniques thatallow PON 10 to reestablish the association of assigned IP addresses toclients 36. Network nodes 11 may monitor PON 10 for networkdisablements. For example, network nodes 11 may send periodic messagesto PON interface 13 to communicate the state of PON interface 13. Theseperiodic messages are sometimes referred to as “keepalives” or “hellos.”When a network node 11 does not receive a response message from PONinterface 13 within an allotted time frame, network node 11 may concludethat a network disablement has occurred. Upon detection of a networkdisablement, network nodes 11 store association information 38 innon-volatile memory for retrieval when PON interface 13 recovers.

[0044] Network nodes 11 may reestablish the address associations uponrecovering from the network disablement. In one embodiment, networknodes 11 retrieve address association information 38 from thenon-volatile memory upon PON 10 recovering from the network disablement.In accordance with the address association information, network nodes 11may associate network addresses to clients 36, and verify whether all ofthe address associations still exist. The recovered address associationinformation 38 may include remaining lease time information such as theamount of lease time remaining for each leased IP address at the time ofthe network disablement.

[0045] Network nodes 11 periodically send ARP queries for the IPaddresses to the associated clients 36 in order to verify the existenceof the address association. Network nodes 11 may send the ARP queriesperiodically for the extent of the remaining lease time indicated inaddress association information 38. For instance, address associationinformation 38 may associate an assigned IP address with a particularclient 36. Network node 11 may periodically send an ARP query for the IPaddress to the particular client 36 for the duration of the remaininglease time to verify that the client has not already released theaddress, e.g., by voluntarily releasing and renewing.

[0046] Network nodes 11 receive ARP responses from clients 36. The ARPresponses demonstrate that the address associations are still present,and network nodes 11 maintain the associations of IP addresses to theclients 36 from which an ARP response is received. Network nodes 11 mayupdate an ARP cache (not shown in FIG. 2) that maps assigned IPaddresses to MAC addresses for clients 36 using information from addressassociation information 38. Network nodes 11 may further communicateinformation regarding existing associations to PON interface 13. PONinterface 13 may use the information to generate routing information.For example, PON interface 13 may associate IP addresses withcorresponding network nodes 11, and associate IP addresses withcorresponding PON interface modules 34. In this manner, PON 10reestablishes the associations of IP address to clients, and may furtherassociate IP addresses to routes through PON 10.

[0047] Network nodes 11 continue to send ARP queries for the IPaddresses until an ARP response is not received, or the remaining leasetime indicated by the association information expires. Network nodes mayfurther cease ARP queries in response to detecting other DHCP messagesthat modify the associations, such as new DCHP acknowledgement, a DHCPrenewal or a DHCP client release. For example, a network node 11 maydetect a new DCHP acknowledgement with an IP address that is currentlyassociated with a different client 36. In response to the new DHCPacknowledgment, network node 11 may modify the address associationinformation to reflect the association change. More specifically,network node 11 may associate the leased IP address with a new client 36for a new lease time, and cease ARP queries for the IP address.

[0048] If an ARP response is not received for a particular client 36,node 11 determines that the applicable network address association is nolonger valid. In this case, if the client requires an IP address, theclient 36 transmits a DHCP request to the node 11 representing theclient. Network node 11 passes the DHCP request to the corresponding PONinterface module 34, which generates a DHCP proxy request on behalf ofthe client 36 to obtain a new address from an appropriate DHCP server.

[0049] In another embodiment, a timing device may be provided todetermine the length of a PON outage. For example, PON 10 may haveaccess to a timing device, such as a real-time clock, to explicitlytrack the length of time of the disablement of PON 10. Network nodes 111may determine the amount of time during which PON 10 was disabled. Forexample, network nodes 11 may set a timestamp in address associationinformation 38 defining the time of the network disablement.

[0050] Upon PON 10 recovering from the disablement, network nodes 11retrieve address association information 38. In this embodiment, networknodes 11 also may compare the timestamp recorded in address associationinformation 38 with the time indicated by the timing device to determinethe length of time of the disablement. Network nodes 11 may updateaddress association information 38 to reflect the length of disablement.

[0051] More particularly, network nodes 11 may update the remaininglease time in address association information 38. For example, networknodes 11 may reduce the remaining lease times of address associationinformation 38 by the length of time of the disablement. Network nodes11 may reestablish the associations of network addresses to clients inaccordance with the updated address association information 38.

[0052] When one or more of the network address leases expire during thenetwork disablement, network nodes 11 may cancel the associationmaintained by address association information 38. Network nodes 11 mayfurther communicate at least a portion of association information 38 toPON interface 13 for generating routing information.

[0053]FIG. 3 is a block diagram illustrating an exemplary addressassociation data structure 40 for one arrangement of address associationinformation 38. In the example of FIG. 3, address association datastructure 40 is a table in which each row represents an IP addressassociation maintained by one of network nodes 11. The invention is inno way limited to the data structure depicted in FIG. 3. Rather, datastructure 40 is provided for purposes of illustration.

[0054] As shown in FIG. 3, for each IP address association, addressassociation data structure 40 may include a leased IP address, a MACaddress corresponding to the client 36 leasing the IP address, and alease time that indicates the remaining time, in seconds, of the IPaddress lease. In the example of FIG. 3, the IP addresses assigned toclient 36 belong to the same IP subnet scope, i.e., the class C subnet192.122.15.x. A first ISP may serve the Class C subnet of the assignedaddresses. However, more than one ISP may assign network addresses tothe clients 36 represented on a single node 11. In that case, the IPaddresses of address association data structure 40 may be IP addressesfrom different IP subnets.

[0055] Upon detecting a network disablement, each of network nodes 11stores data structures, similar to address association data structure 40of FIG. 3, for the clients 36 represented by the network node. Networknodes 11 use the address association information 38 of addressassociation data structures 40 to reestablish address associations uponrecovery from the network disablement. Network node 11 may verifyaddress associations by sending an ARP query for each of the leased IPaddresses in address association data structure 40. For instance,network node 11 may send an ARP query for assigned IP address128.15.122.129 periodically for 400 seconds. The ARP queries may be sentto client 36 corresponding to MAC address 00-01-02-5F-B0-42. The data ofFIG. 3 is illustrated for exemplary purposes, and may be readily varied.For example, address association data structure 40 may further include asubnet mask associated with clients 36, a network address for a DHCPserver 37 that assigned the IP address, or the like.

[0056]FIG. 4 is a flow diagram illustrating a technique for maintainingaddress associations in accordance with an embodiment of the invention.As shown in FIG. 4, network nodes 11 maintain address associationinformation 38 by monitoring DHCP communications between clients 36 andDHCP severs 37 (42). For example, a network node 11 may detect a DHCPacknowledgement from one of DHCP servers 37. The DHCP acknowledgementmay include an assigned IP address and a lease time for the assigned IPaddress. The DHCP acknowledgement may further include a MAC addresscorresponding to client 36 requesting the IP address. The network node11 that represents the requesting client 36 may add an entry in addressassociation information 38 to associate the assigned IP address to therequesting client 36 for the defined lease time.

[0057] Network nodes 11 concurrently monitor for a network disablement(44). For example, network nodes 11 may send periodic messages, e.g.keepalive messages, to PON interface 13 to communicate the state of thenetwork node devices. When a response to one of the periodic message isnot received within an allotted time frame, network nodes 11 mayconclude a network disablement has occurred. When no network disablementis detected, network nodes 11 continue to maintain accurate addressassociation information 38.

[0058] When a network disablement is detected, network nodes 11 storethe current address association information 38 in non-volatile memory(48) for later retrieval. Network nodes 11 monitor PON 10 to determinewhether PON 10 has recovered from the network disablement (50), e.g., bylistening for responses from PON interface 13 to keepalive messages thatare periodically sent. Upon PON 10 recovering from the networkdisablement, network nodes 11 retrieve address association information38 from the non-volatile memory, and reestablish the addressassociations in accordance with address association information 38 (52,54).

[0059]FIG. 5 is a flow diagram illustrating a technique forreestablishing address associations upon recovery of a PON from anetwork disablement. Upon retrieving address association information 38,network node 11 may associate a network address to a client 36 inaccordance with address association information 38 (55). To verify theexistence of the association, network nodes 11 may send ARP queries foreach of the IP addresses in address association information 38 (56). Forexample, for each assigned IP address association, network node 11 mayperiodically send an ARP query for the IP address for the remainder of alease time. Network node 11 may send the ARP query to client 36 thatcorresponds with a MAC address in address association information 38.When an ARP response is not received from client 36 associated with theIP address, network node 11 cancels the association between the IPaddress and client 36 (58, 60).

[0060] When an ARP response is received from client 36 associated withthe IP address, network node 11 maintains the association between the IPaddress and client 36 (62). Network node 11 determines whether any DHCPcommunications from client 36 or DHCP servers 37 modify addressassociation information 38 (64). For example, network nodes 11 may lookfor DHCP acknowledgments, DHCP renewals, and DHCP address releases. Whennetwork node 11 detects a DHCP communication that modifies associationsnetwork node 11 modifies the association (66). Modifying the associationmay include canceling associations, associating a network address with adifferent one of clients 36, resetting a lease time for an addressassociation, or other modification.

[0061] When network node 11 does not detect a DHCP communication thatmodifies network address associations, network node 11 checks whether alease time of the association has expired (68). When the lease time ofthe network address association has expired, network nodes 11 cancel theassociation between the IP address and client 36 (60). When the leasetime of the association has not expired, network nodes 11 continue tosend ARP queries periodically for the IP address of the association.

[0062]FIG. 6 is a flow diagram illustrating a technique forreestablishing address associations using a timing device upon recoveryof a PON from a network disablement. Upon retrieving address associationinformation 38, network nodes 11 determine the length of time of thedisablement of PON 10 (70). For example, network nodes 11 may compare atimestamp recorded in address association information 38 with areal-time clock to determine the length of time PON 10 was disabled. Thereal-time clock may be provided within each network node 11. In thiscase, the time indicated by the real-time clock may be locally retrievedby a network node. Alternatively, the real-time clock may be providedwithin a single network node 11 or within PON interface 13. In thiscase, the time indicated by the real-time clock may be communicatedwithin messages transmitted on PON 10.

[0063] Network nodes 11 compare the disablement length with a remaininglease time of the association to determine whether the IP address leaseexpired during the network disablement (72). The lease time in addressassociation information 38 indicates the amount of time left in the IPaddress lease at the beginning of the network disablement. Lease timesthat are shorter than the disablement length indicate leases thatexpired during the duration of the network disablement. When the leasetime of the assigned IP address is shorter than the disablement length,network node 11 cancels the association between the IP address andclient 36 (74).

[0064] When the lease time of the assigned IP address is not shorterthan the disablement length, network node 11 updates the lease time forthe assigned IP address (76). For example, network node 11 may subtractthe disablement length from the lease time of the assigned IP address toobtain an adjusted lease time. Network node 11 may associate the IPaddress to client 36 in accordance with the adjusted lease time (78).

[0065] In various embodiment, the invention also is directed to acomputer-readable medium comprising instructions to cause a processor toperform the techniques described herein. The instructions may be storedon a variety of computer-readable media including but not limited toROM, EEPROM, RAM, Flash memory, magnetic or optical data storage disksor tapes, or similar media.

[0066] Various embodiments of the invention have been described. Theseand other embodiments are within the scope of the following claims.

1. A method comprising: detecting a disablement of a passive opticalnetwork; storing address association information indicating associationof network addresses with network clients upon detecting thedisablement; and associating the network addresses and the networkclients based on the stored address association information uponrecovery from the disablement.
 2. The method of claim 1, whereinassociating the network addresses and the network clients includes:retrieving the stored address association information; and verifyingwhether the associations indicated by the address associationinformation are valid.
 3. The method of claim 2, wherein verifyingwhether the associations are valid includes: sending Address ResolutionProtocol (ARP) queries for the network addresses indicated by theaddress association information; and maintaining the addressassociations upon receiving ARP responses.
 4. The method of claim 3,wherein the address association information includes a remaining leasetime, the method further comprising sending the ARP queries periodicallyfor the remaining lease time for each of the address associations. 5.The method of claim 4, further comprising ceasing the sending of the ARPqueries for one of the network addresses upon detecting a change in theaddress association information for the respective network address. 6.The method of claim 3, further comprising canceling the addressassociation for one of the network addresses when an ARP response is notreceived for the respective network address within a predeterminedperiod of time.
 7. The method of claim 3, further comprising sending theARP query to a network client associated with the network address. 8.The method of claim 2, further comprising modifying the addressassociation information upon detecting a lease of one of the networkaddresses.
 9. The method of claim 2, further comprising modifying theaddress association information upon detecting a renewal of one of thenetwork addresses.
 10. The method of claim 2, further comprisingcanceling one of the address associations upon detecting that one of theclients has released the respective network address.
 11. The method ofclaim 1, further comprising: tracking a length of time of the networkdisablement; and updating remaining lease times of address associationinformation in accordance with the length of time of the networkdisablement.
 12. The method of claim 11, wherein tracking the length oftime of the network disablement includes: setting a timestamp upondetecting the network disablement; and comparing the timestamp with atime indicated by a timing device to determine the length of time of thenetwork disablement.
 13. The method of claim 11, wherein updatingremaining lease times includes subtracting the length of time of thenetwork disablement from the remaining lease times.
 14. The method ofclaim 12, further comprising canceling one of the associations when theremaining lease time for the respective association is shorter than thelength of time of the network disablement.
 15. The method of claim 1,wherein detecting a network disablement includes: sending periodicmessages to communicate the state of the passive optical network; andconcluding that a network disablement has occurred when a response tothe periodic messages is not received with a predetermined period oftime.
 16. The method of claim 1, wherein the address associationinformation includes a network address and a remaining lease time. 17.The method of claim 1, wherein storing network address associationinformation includes storing the network address association informationin non-volatile memory.
 18. The method of claim 1, wherein the networkaddresses include Internet Protocol (IP) addresses.
 19. The method ofclaim 1, further comprising leasing the network addresses to clients fora specified duration of time.
 20. A computer-readable medium comprisinginstructions to cause a processor to: detect a disablement of a passiveoptical network; store address association information indicatingassociation of network addresses with network clients upon detecting thedisablement; and associate the network addresses and the network clientsbased on the stored address association information upon recovery fromthe disablement.
 21. A method comprising: retrieving stored addressassociation information indicating association of network addresses withnetwork clients upon recovery of a passive optical network from adisablement; associating the network addresses to clients based on thestored address association information; sending ARP queries for thenetwork addresses indicated in the address association information; andmaintaining the associations upon receiving ARP responses for thenetwork addresses.
 22. The method of claim 21, wherein sending ARPqueries for the network addresses indicated in the address associationinformation includes periodically sending ARP queries for the networkaddresses for a period of time.
 23. The method of claim 22, wherein theperiod of time includes a remaining lease time indicated for each of thenetwork addresses in address association information.
 24. The method ofclaim 21, further comprising: updating the address associationinformation for at least one of the network addresses; and ceasing theARP queries for network addresses that have association information thatwas updated.
 25. The method of claim 21, further comprising cancelingthe association of a network address to a client upon expiration of aremaining lease time.
 26. The method of claim 21, further comprising:detecting a lease modification message; and updating the associationinformation upon detecting a modification message.
 27. The method ofclaim 26, wherein the lease modification message includes at least oneof an acknowledge message indicating a new lease of one of the networkaddresses, a renewal message indicating a new lease time for a networkaddress, and a client release message indicating that one of the clientshas released one of the leased addresses.
 28. A computer-readable mediumcomprising instructions to cause a processor to: retrieve stored addressassociation information indicating association of network addresses withnetwork clients upon recovery of a passive optical network from adisablement; associate the network addresses to clients based on thestored address association information; send ARP queries for the networkaddresses indicated in the address association information; and maintainthe associations upon receiving ARP responses for the network addresses.29. A method comprising: retrieving stored address associationinformation upon recovery of a passive optical network from adisablement; determining a length of time of the disablement; updatingremaining lease times indicated by the address association informationin accordance with the determined length of time of the networkdisablement; and associating the network addresses to the networkclients in accordance with the updated address association information.30. The method of claim 29, wherein determining the length of time ofthe network disablement includes: setting a timestamp upon detecting thenetwork disablement; and comparing the timestamp with a timing device todetermine the length of time of the network disablement.
 31. The methodof claim 29, wherein updating the remaining lease times includessubtracting the length of time of the network disablement from theremaining lease time.
 32. The method of claim 29, further comprisingcanceling the association from the address association information whenthe remaining lease time is shorter than the length of time of thenetwork disablement.
 33. The method of claim 29, wherein the networkaddresses include Internet Protocol (IP) addresses.
 34. The method ofclaim 29, further comprising: detecting a network disablement of apassive optical network; and storing address association informationupon detecting a network disablement.
 35. The method of claim 29,further comprising canceling the association of a network address to aclient upon the remaining lease time expiring.
 36. A computer-readablemedium comprising instructions to cause a processor to: retrieve storedaddress association information indicating association of networkaddresses with network clients upon recovery of a passive opticalnetwork from a disablement; associate the network addresses to clientsbased on the stored address association information; send ARP queriesfor the network addresses indicated in the address associationinformation; and maintain the associations upon receiving ARP responsesfor the network addresses.
 37. A passive optical network comprising: anetwork node that represents at least one client; an interface thattransmits information to the network node via an optical fiber link; anda set of address association information associated with the networknode that associates network addresses to the clients represented by thenode upon recovery of the passive optical network from a disablement.38. The passive optical network of claim 37, wherein the network nodestores the set of address association information in a non-volatilememory upon detecting the passive optical network disablement.
 39. Thepassive optical network of claim 37, wherein the address associationinformation includes assigned network addresses and a remaining leasetime of the assigned network address.
 40. The passive optical network ofclaim 39, wherein the network node sends an ARP query the networkaddresses to the associated client for the duration of the remaininglease time indicated by the address association information.
 41. Thepassive optical network of claim 37, further comprising a timing device.42. The passive optical network of claim 41, wherein the network nodecompares a timestamp with a time indicated by the timing device todetermine the length of time of the network disablement.
 43. A passiveoptical network device comprising: means for detecting a disablement ofa passive optical network; means for storing address associationinformation indicating association of network addresses with networkclients upon detecting the disablement; and means for associating thenetwork addresses and the network clients based on the stored addressassociation information upon recovery from the disablement.
 44. Thedevice of claim 43, wherein associating the network addresses and thenetwork clients includes: means for retrieving the stored addressassociation information; and means for verifying whether theassociations indicated by the address association information are valid.45. The device of claim 44, wherein the means for verifying whether theassociations are valid includes: means for sending Address ResolutionProtocol (ARP) queries for the network addresses indicated by theaddress association information; and means for maintaining the addressassociations upon receiving ARP responses.
 46. The device of claim 45,wherein the address association information includes a remaining leasetime, wherein means for sending the ARP queries periodically sends theARP queries for the remaining lease time for each of the addressassociations.
 47. The device of claim 45, wherein the means for sendingthe ARP queries ceases the sending of the ARP queries for one of thenetwork addresses upon detecting a change in the address associationinformation for the respective network address.
 48. The device of claim45, further comprising means for canceling the address association forone of the network addresses when an ARP response is not received forthe respective network address within a predetermined period of time.49. The device of claim 45, further comprising means for sending the ARPquery to a network client associated with the network address.
 50. Thedevice of claim 44, further comprising means for modifying the addressassociation information upon detecting a lease of one of the networkaddresses.
 51. The device of claim 44, further comprising means formodifying the address association information upon detecting a renewalof one of the network addresses.
 52. The device of claim 44, furthercomprising means for canceling one of the address associations upondetecting that one of the clients has released the respective networkaddress.
 53. The device of claim 43, further comprising: means fortracking a length of time of the network disablement; and means forupdating remaining lease times of address association information inaccordance with the length of time of the network disablement.
 54. Thedevice of claim 53, wherein the means for tracking the length of time ofthe network disablement sets a timestamp upon detecting the networkdisablement, and compares the timestamp with a time indicated by atiming device to determine the length of time of the networkdisablement.
 55. The device of claim 43, wherein the address associationinformation includes a network address and a remaining lease time. 56.The device of claim 43, wherein the network addresses include InternetProtocol (IP) addresses.